Here I will explain this to you guys:
The concept of rank ie bronze silver gold, is simply Riot putting color on something more simplistic to keep their hoard of man-children entertained and satisfied.
For example, if a person makes a new account, they can win their first 5 games and be iron or bronze in rank but matched with gold or low plat. Why is this? Because rank is not matched to rank. Rank is just an image.
LP gains are a number that represents "real elo"(yes "elo" is an actual statistical tool that can be applied to create a ranked ladder) times some multiplier that represents one's rank vs the rank of their competition and teammates. If your rank is iron 4 for example and you are playing in a game where everyone else is appx. rank gold 1, then that multiplier would be higher, so one would see higher LP gains. The LP gains are how "real elo"(what isn't plainly seen) and "rank"(riot's coloring book for u) interact.
This concept somehow perpetually eludes most 27 year-olds on welfare who spend most their time bitching about online video games. Matchmaking is fair, you are all just ignorant and need something to blame for your heart-breaking video game losses.